Fluorescent whitening agents



2,737,516 Patented Mar. 6, 1956 k a "2,737,516 1 FLUORESCENT WHITENINGAGENTS Mario Francesco Sartori, Wilmington, Del.,'assignor to E. I. duPont de Nemours and Company, Wilmington, DeL, a corporation of DelawareNo Drawing. Application May 2, 1955 Serial No. 505,559

6 Claims. Cl. 260-304) ,This invention relates to the production ofnovel organic compounds which are useful as whitening agents for variousfibrous materials, including cellulosic fibers and nylon. It is anobject-of this invention to produce compounds-of the above generalnature, but which are characterized further by bleach fastness and bycorrect shade of fluorescence. Additional objects and achievenients ofthis invention will appear as the description proceeds.

'The art of whitening or brightening textile'fiber and paper is ofrelatively recent development. It has been found that fibrous materialswhich normally have a dull, yellowish cast when in the white, unbleachedstate, become whiter and brighter if treated with agents which fluoresceunderultraviolet light. Presumably the action of the ultraviolet rayspresent in ordinary daylight is sufiicient to excite these agents uponthe fiber to emit fluorescence which overcomes the undesirable tinge ofcolor in the unbleached fiber. Best results are obtained when the shadeof fluorescence is complementary to that of the unbleached fiber, sothat the colors will cancel out each other. Since the most commonoff-white shade of unbleached cellulosic and nylon fibers is yellowish,the most desirable shade in a fluorescent is blue.

Another very important demand developed by the trade is bleach fastness.Inasmuch as the aforementioned fluorescent agents are generallyincorporated into soap and synthetic detergents, which are packaged andmarketed for household use, and'inasmuch as in household practicelaundered articles are often subjected to bleaching with various agents,for instance hypochlorites, it is essential that the fluorescenttransferred from the detergent to the fiber shall not berremoved ordestroyed by the action of bleach. Unfortunately, most of thefluorescent agents now on the market, and having the desirable blueshade, are weak in respect to this qualificatiofi o'f bleach resistance.I

In addition to the above two primary qualifications, anagent for thepurposes of this invention should be capable of being synthesizedeconomically from readily available materials, and should havesuflicient fluorescent power (often referred to as tinctorial strength)to give the desired efiect at a minimum cost. It should also haveaflinity for the fibers to which it is applied, and should be capable ofbeing dispersed readily in water in the concentrations that wouldnormally be used in the treatment of nylon or cellulosic fibers.

a Now according to my invention. new chemical compounds are synthesizedwhich satisfy to an excellent degree all the aforegoing qualifications.The novel compounds 'of this invention may be defined by the generalformula wherein X stands for O, S or NH; Y represents a sulfo group, andn is zero or one.

According to accepted nomenclature, they may be named collectively as2-[p-(2-benzazolyl)phenyl]- naphth[1,2]oxazole.s and their monosulfoderivatives.

These compounds may be synthesized by condensing the correspondingp-2-benzazolyl)-benzoic acid of formula with l-amino-Z-naphthol or amonosulfo-derivative thereof by the aid of an acid halogenating agent,such as phosphorus oxychloride, phosphorus trichloride or thionylchloride, in a suitable liquid medium and at moderatetemperature, say toC., to form an intermediate condensation product, presumably anorthohydroxy amide, and .then ring-closing the latter into anaphthoxazole compound, by heatingat a higher temperature, say in thevicinity of to 220 C. As suitable liquid meditnn, a high-boiling, inertorganic solvent is recommended, for instance trichlorobenzene, diphenylether, or alphaor beta-methyl naphthalene. For the amide formation step,inert organic liquids of somewhat lower boiling point are also suitable,for instance pyridine.

The monosulfonated product may be prepared by sulfonating the productobtained as above from l-arnino- Z-naphthol, or by starting initiallywith a monosulfonatedl-amino-Z-naphthol. Sulfonation of the condensedproduct is readily achieved by treating the same with sulfuric acidmonohydrateyat room temperature.

Without limiting this invention, the following examples are given toillustrate my preferred mode of operation. Parts mentioned are byweight.

EXAMPLE 1- 2- [p-(Z-benzimidazolyl)phenyl] -napl zth [1,2] oxazole Asuspension of 2.6 parts of p-(2-benzimidazolyl)- benzoic acid (Ann. 205,118), 2 parts of 1-amino-2- naphthol hydrochloride and 1.8 parts ofphosphoryl chloride in 30 parts of trichlorobenzene was heated at 125C(for 1 hour and then at 200 C. for 5 hours.

After cooling to room temperature, the precipitate was filtered off andwashed with petroleum ether. The gray filter cake was slurried at 50 C.with an excess of 5% sodium carbonate aqueous solution, filteredhot,washed and dried. Cream-colored crystals of M. P. 292 C. were obtained.The absorption maximum of this compound in dimethylformamide is locatedat 364 millimicrons.

Analysis.Calc. for C24H15ON3: C, 79.5; H, 4.1; N, 11.6. Foundz C, 79.6;H, 4.1; N, 12.3.

EXAMPLE 2 2-[p-(2-benzimidazolyl) phenyl] -mzphth [1,2 oxazole sodiumsulfonate 5 parts of the product prepared in Example 1 were dissolved in50 parts of sulfuric acid monohydrate and stirred at room temperature.When a test portion ofthe sulfonation mixture dissolved to give a clearsolution in dilute sodium carbonate, the reaction mixture was pouredinto 500 parts of iced water. The precipitate was filtered off andwashed. The yellow filter cake was dispersed in water,.the dispersionwas made alkaline with sodium carbonate to form a solution and theproduct was finally precipitated by adding sodium chloride.

The pale yellowish precipitate was filtered off, washed thecornpound indimethylformamide is located at 365 millimicrons.

EXAMPLE 3 A suspension of-2.6 parts of-p-(2-benzimidazolyl)benzoic acid,2.4 parts of 1-amino-2-hydroxy-4-naphthalenesulfonic acid and 1.7 partsof phosphoryl chloride in parts of pyridine was heated at 70 C. for 1hour and then at 110 C. for. 3 hours. After cooling to room temperature,the mixture was drowned in water, made acid to Congo red withhydrochloric acid and'filtered. The filter cake (o-hydroxy-amide) wasfirst washed with cold water, then with ethyl alcohol. and dried. Thecrude product thus obtained was slurried in parts of trichlorobenzeneand heated at.200 C. for 8 hours. After cooling to room. temperaturethe'precipitated product was filtered off, washed. withpetroleum: ether,dissolved in dimethylformamideandi then reprecipitated by adding anequal weight of an aqueous, 10% salt solution. The product has theformula The water solution of this compound exhibits a strong bluefluorescence. The. absorption maximum of this compound indimethylformamide is located at 365 millimicrons.

A mixture of 4.5 partsof' p-(2-benzothiazolyl)benzoic acid (Chem. News,124,. 393), 3 parts of 1-amino-2- naphthol hydrochloride and 2.8 partsof phosphoryl chloride was condensed following the method described inExample 1 for the preparation. of the analogous benzimidazolederivative. Cream colored crystals of M. P. 256 C. were obtained.

Analysis-Cale. for C24H'i4N2SO: C, 74.2; H, 3.6; N; 7.4; S, 83. Found:C,. 75.2; H, 3.4; N, 7; S, 8.

The absorption maximum of this compound in dimethylformamide is locatedat 368 millimicrons.

EXAMPLE 5 Uponsulfonation of the product of,Example 4 by the methoddescribed in Example2, 2- [p-(2-benzothiazolyl)phenyll-naphthl1,2]oxazole' sodium sulfonate was ob-v tained. It is apale yellowishpowder, soluble in dilute sodium carbonate,. and havingtheformula fluoresces blue, and its absorption maximum is located at 370millimicrons..

EXAMPLE 6 2- [p- (2-benz0xaz0lyl) phenyl] -naph th [1,2 loxazole Asuspension of 2.6 partsof. p;(Z-benzoxazolyDbenzoic acid,(preparedas,described.below.), 2parts of 1 -amino-2- naphthol hydrochloride and1.7 parts of phosphoryl chloride was condensed following the proceduredescribed in Example 1. Pale yellowish crystals of M. P. 320325 C. wereobtained.

Analysis.-Calc. for C24H14O2N2: C, 79.2; H, 3.85; N, 7.7. Found: C,79.8; H, 3.9; N, 7.4.

The initial p-(2-benzoxazolyl)benzoic acid was prepared as follows: Asuspension of 20 parts of methylhydrogen terephthalate and 11 parts oforthoaminophenol in 110 parts of trichlorobenzene was heated at C. for 3hours and at 200 C. for 16 hours. After cooling to room temperature thereaction mass was filtered and washed with petroleum ether. The filtercake was slurried in 500 parts of water containing an excess of sodiumcarbonate, the slurry was boiled for 5 minutes and filtered hot. Afterclarification with activated carbon the filtrate was made acid withacetic acid. The white precipitate was filtered off, washed at 50 C.with ethanol andgd'ried. A white powder of M. P. above 300 C. wasobtained.

EXAMPLE 7 2- [17 (2-benz0xaz0lyl) phenyl] -naphth [1,2 1 oxazole sodiumsulfonate N N SO;N8

o -o O EXAMPLE 8 2- [p-(Z benzoxazolyl ph enyl] -naphth [1,2 0xazole 5-sodium sulfonate 5.3.parts of 2-(p-benzoxazolyl)benzoic acid werecondensed with 4.8 parts of 1-amino-2-hydroxyr4-naphthalene-sulfonicacid and 3.4 parts of phosphoryl chloride in pyridine, ring-closed andpurified: according to the procedure described in Example 3.

A yellowish powder, completely soluble in dilute sodium carbonatesolutionwas obtained. The water: solution of. the sodium salt ofthiscompound exhibits bluish fluorescence.

The novel products of the foregoing several examples weretested forwhitening power and bleach resistance-by the sametests as-described inmy copending application Serial No. 333,016, filed January 23, 1953(Patenu'No; 2,715,632, issued August 16, 1955), and found. to besatisfactory in. both respects. The fluorescence imparted to a sample ofcotton fabric by the novel agents. was

retained'in full (essentially in the bleach-.fastness test.

Tests for light-fastness, substantivity and washrfastness were alsocarriedrout, and-showed my novel compounds to. compare. favorably inrespect to these qualities with the best. fluorescents which are now onthe market.

The monosulfonated products are useful for cotton fiber. Theunsulfonated ones can be used both'onicotton and on nylon.

The compounds given in the above examples havebeen isolated as thesodium salts of the sulfonic acids., By using potassium hydroxide andpotassium salts in lieu of sodium hydroxide and sodium salts,throughout, the productsmay be obtained as potassium sulfonates.Isolation as the free sulfonic acids can be efiFected by acidificationof the condensation mass, andthe products thus obtained may be reactedwith ammonium hydroxide or any suitable organic or inorganic base, toyield the corresponding salt.

In addition to producing a whitening effect upon textile material orpaper, my novel compounds may also be used for various other purposeswhere fluorescence or absorption of ultraviolet light is desirable, forinstance to achieve fluorescent effects in costumes or stage settings,to achieve novel eifects on photographic paper, as ultraviolet filterswhen impregnated on cellulosic films which are used for Wrappingmaterials, etc.

I claim as my invention:

1. A compound of the group consisting of 2-[p-(2-benzimidazolyDphenyl]-naphth[1,2]oxazole, 2 [p (2benzothiazolyl)phenyl]-naphth[1,2]oxaz0le, 2 [p (2benzoxazolyDphenyl]-naphth[1,2]oxazole and t h e i r monosulfoderivatives.

2. 2 [p (2 benzimidazolyDphenyl] naphth[1,2]oxazole.

3. The S-sOdium-sulfonate of 2-[p-(2-benzimidazolyl) phenyl] -naphth1,2] oxazole.

4. A sodium monosulfonate of 2-[p-(2-benzothiazolyl) phenyl] -naphth[1,2] oxazole.

5. A sodium monosulfonate of 2-[p-(2-benzoxazolyl) phenyl] -naphth 1,2]oxazole.

6. The process of producing a fluorescent agent which comprisescondensing a carboxylic acid of the group consisting ofp-(Z-benzimidazolyl)benzoic acid, p-(Z-benzothiazolyl)benzoic acid, andp-(2-benzoxazolyl)benzoic acid, in an inert organic liquid and in thepresence of an acid halogenating agent, with an ortho-amino-naphthol ofthe group consisting of 1-amino-2-naphthol and l-amino-2-naphthol-4-sulfonic acid to give an intermediate condensation product,and further heating the said intermediate condensation product in aninert organic liquid to effect conversion thereof into an oxazolecompound.

No references cited.

1. A COMPOUND OF THE GROUP CONSISTING OF2-(P-(2BENZIMIDAZOLYL)PHENYL)-NAPHTH(1,2)OXAZOLE,2-(P-(2BENZOTHIAZOLYL)PHENYL)-NAPHTH(1,2)OXAZOLE,2-(P-(2BENZOXAZOLYL)PHENYL)-NAPHTH(1,2)OXAZOLE AND THEIR MONOSULFODERIVATIVES.